Tuesday, January 20, 2009

WANTED: STATISTICAL DATA ANALYSIS HELP

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The following is a graph of the latest and greatest version [ERSST.v3b] of NINO3.4 and Southern Ocean SST anomalies. It’s always struck me that there was an underlying component of the Southern Ocean SST anomalies in the NINO3.4 SST anomaly data, but proving it is beyond my capabilities. Even though I’d be reprimanded for it, the best I could do would be to put a 6th-order polynomial trend line of the NINO3.4 data on the graph and say, “Hmm, that looks like it fits,” which is exactly what I’ve done in that graph.

5 comments:

Bill Illis
said...

Bob, this looks interesting.

Let's think about this (and ocean data in general) in physical terms. What is really going on here? What physical ocean current(s) changes are driving this climate phenomenon? How can this physically effect some climate index in justifiable terms.

In this case, the cold upwelling water than sometimes drives the ENSO (depending on the Trade Winds in my opinion and the NCEP analysis as well), that cold/warm upwelling water actually originates from the southern ocean and circulates up the south american pacific coast (and there is different effects depending on the depths of ocean currents in question.)

The ENSO region ocean water originates from the southern ocean.

In fact, there is a negative correlation of the ENSO with southern hemisphere temperatures (when you just use the ENSO as a variable or even the AMO and exclude the southern ocean SSTs, there is literally a negative correlation). This is not expected since we all know the ENSO has a huge impact on temperatures. Why would it be negatively correlated with southern temperatures?

It would be if the southern ocean temperatures are a pre-cursor to the ENSO. Cold southern ocean temps along South America eventually circulate up to the ENSO region and if the Trades are just right, that cold water eventually upwells into the ENSO region - the warm water eventually influences the ENSO region ocean SSTs.

Timelines would be a few months or several years but there would still be El Ninos here and there and La Ninas here and there, it is just that there might be more El Ninos when the southern ocean is warmer and more La Ninas when the southern ocean is cooler.

Just try a few lags (1 month, 2 months, ... maxing out at 24 months) and see how much correlation there is.

You don't have to worry about 6th order polynomials, is there a simple correlation or not.

I think the correlations extending out over many years are not justifiable on physical terms and one should just stick with the lowest timelines which produce significant correlations.

Unfortunately, the ERSST.v3b version of the NINO3.4 SST anomaly data begins in 1900. Here’s it’s curve. It’s the same as the one I used in the post above, without the Southern Ocean data superimposed. In it, I see an underlying trend that decreases from 1900 to 1910, then rises almost continuously (there’s a jog in it in the 1940s) until the late-1980s, early-1990s, when it begins to flatten. Then it decreases in trend sharply. That’s the same explanation I’d use for the Southern Ocean curve above.http://i43.tinypic.com/30a5req.jpg

In addition to that, the amplitude of the NINO3.4 anomalies decrease in the 1930s. There’s the large multiyear El Nino in the early 1940s, after which the amplitude decreases again until the 1950s. It starts to increase again and remains high through the 1997/98 El Nino. The frequency also appears to change after the 1950s too.

I don’t know how one would differentiate it, but I’m not trying to show that the “spikes” in the Southern Ocean SST anomalies precede those of ENSO events; I’m more interested in the underlying trends in the SST anomaly of the NINO3.4 SST anomalies.

I can decrease the vertical axis of the comparative graph of NINO3.4 and Southern Ocean SST anomalies that I used in the post.http://i40.tinypic.com/212fmeq.jpg

The 6th-order polynomial trend of the NINO3.4 data does a good job of following the Southern Ocean, but the statistical types complain about the use of poly trends. They use all sorts of analysis tools, but I haven’t the foggiest idea of what they’re talking about or how to use them. It’s that type of comparative analysis I’m looking for.

Bill: You wrote, “In fact, there is a negative correlation of the ENSO with southern hemisphere temperatures (when you just use the ENSO as a variable or even the AMO and exclude the southern ocean SSTs, there is literally a negative correlation). This is not expected since we all know the ENSO has a huge impact on temperatures. Why would it be negatively correlated with southern temperatures?”

Are you talking about how some South Pacific SST anomalies at specific mid-latitudes drop when NINO 3.4 SST anomalies rise? If not, do you have a graph of what you’re talking about?

Also, I did a comparison of Southern Ocean, Southeast South Pacific, and NINO3.4 SST anomalies in the poorly titled post “Looking for the Source of ENSO”.http://bobtisdale.blogspot.com/2008/06/looking-for-source-of-enso.htmlI’ll have to go back and look at that in more detail. And I’ve also plotted Southern Ocean and NINO3.4 SST anomalies but never posted the comparison. I might’ve gotten sidetracked with another series of posts. It happens. It would be best for me to redo it anyway with the updated ERSST.v3b data.

Off topic, but related to ENSO: The more I think about the suppression of El Nino events by volcanic eruptions, the more I wonder whether the 1997/98 El Nino would have even occurred if the heat distribution processes of the 1982/83 El Nino had not been curtailed by El Chichon.

Are “super” El Ninos a function of a significant rise in surface level solar irradiance?

In addition to the Southern Ocean SST anomalies, let’s assume solar is the other primary driver of ENSO events. From the 1960s to ~1975, volcanic eruptions suppressed solar irradiance in the tropics. After 1975, there was that increase in surface level solar irradiance (no more volcanoes till 1982) and the significant rise in TSI from solar cycles 20 to 21. SC21 peaked in 1979, I believe. A few years later, there’s the 1982/83 El Nino, but it got knocked down by El Chichon.

Going back to the start of the 20th Century, there was a gradual increase in the magnitudes of solar cycles from ~1900 to ~1950. Was the multiyear “super” El Nino in the 1940s caused by the gradual build-up of heat in the PWP that resulted from that rise in TSI? Then in the mid-40s there’s the discontinuity that lowered SST anomalies by ~0.3 deg C. Is that across the board? Did it effect NINO3.4 SST anomaly data too? Without that error, would the La Nina period in the mid-40s have leaned more toward El Nino, making that period even more significant as an El Nino cluster? Sorry, just thinking out loud.

About the ENSO being negatively correlated with southern hemisphere temperatures, when I was doing the temp reconstructions using regression on the ENSO and the AMO (with a 3 month lag for the ENSO), I found the coefficient for the ENSO was actually negative for southern hemisphere temperatures (which are partly land temperatures but mostly ocean temperatures.) It was positive for the global temps and tropics temps but negative for the southern hemisphere.

This is not expected at all (a big El Nino results in lower temperatures in the southern hemisphere? No, that is just wrong). This just indicated there was a problem that needed to be addressed. When I started using the southern atlantic temps (as a southern version of the AMO), the coefficient went back to slightly positive as it should have been.

But that points to one of the main characteristics of the ENSO, it is the Trade Winds at the equator which drive the ENSO but it is modulated by southern ocean SSTs. The negative correlation really meant the ENSO was affected BY rather than provided an affect TO southern ocean temps.

Long sustained periods of Trade Winds blow the warm surface water in the ENSO region into the Western Pacific and these surface waters are replaced by cold water from below - and that cold water originates in the southern ocean. It doesn't come down the north american coast, it comes up the south american coast from the southern ocean.

So the southern ocean temps (maybe along the south american coast only rather than the whole southern ocean) might be also be a big driver of the ENSO.

The Trades need to be blowing hard and just right to bring that colder water in from the southern ocean but if it does, then the anomaly of the southern ocean temps is actually a predictor or precursor for the average ENSO conditions expected over the next period of time.

This is exactly what your chart shows.

If the Trades are not blowing, there is less ocean circulation up from below - up the south american coast from the southern ocean and the surface water in the ENSO region gets heated day after day by the equatorial Sun and, voila, we have El Nino.

But if the southern ocean temps are colder than normal, less El Ninos will develop over the next period of time, more La Ninas will develop.

The Trades are still the driving force which allows or blocks the southern ocean waters from making it to the surface in the ENSO region, but the southern ocean anomaly temps are the next biggest contributing factor.

Watch the movie you produced again and the one from the NOAA and you can see this in action.

A simple regression should allow you to tease these out. I don't think it has been done before.

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Comments that are political in nature or that have nothing to do with the post will be deleted.####The Smith and Reynolds SST Posts DOES NOT LIST ALL SST POSTS. I stopped using ERSST.v2 data for SST when NOAA deleted it from NOMADS early in 2009.

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